function calcost() {
document.cost_form.tot1.value = truncent(eval(parseInt(document.cost_form.quan1.value) * parseFloat(document.cost_form.unit1.value)));
document.cost_form.tot2.value = truncent(eval(parseInt(document.cost_form.quan2.value) * parseFloat(document.cost_form.unit2.value))); 
document.cost_form.tot3.value = truncent(eval(parseInt(document.cost_form.quan3.value) * parseFloat(document.cost_form.unit3.value))); 
document.cost_form.tot4.value = truncent(eval(parseInt(document.cost_form.quan4.value) * parseFloat(document.cost_form.unit4.value)));

if (document.cost_form.quan1.value.length < 1) { document.cost_form.tot1.value = eval(0.00) }
if (document.cost_form.quan2.value.length < 1) { document.cost_form.tot2.value = eval(0.00) }
if (document.cost_form.quan3.value.length < 1) { document.cost_form.tot3.value = eval(0.00) }
if (document.cost_form.quan4.value.length < 1) { document.cost_form.tot4.value = eval(0.00) }

document.cost_form.subtotal.value = truncent(eval(parseFloat(document.cost_form.tot1.value) + parseFloat(document.cost_form.tot2.value) + parseFloat(document.cost_form.tot3.value) + parseFloat(document.cost_form.tot4.value)));

if (document.cost_form.gares.checked) {document.cost_form.tax.value = truncent(eval(parseFloat(document.cost_form.subtotal.value) * 0.07)) }
else {document.cost_form.tax.value = 0.00}

document.cost_form.total.value = truncent(eval(parseFloat(document.cost_form.subtotal.value) + parseFloat(document.cost_form.tax.value) + parseFloat(document.cost_form.ship.value)))
}

function truncent(strng) {
if (strng == 0) { return "0.00";} else
{ var str = "" + Math.round(strng * 100);
 return(str.substring(0, str.length-2) + "." + str.substring(str.length-2, str.length)); }
}